Phy 201
The first question I have is: the idea of nonconservative and conservative forces I understand but what I want to know is, what is the work done ON and BY. I presume that ON would be friction, gravity, etc...What is the work done by the system, is that the displacement maybe??
For every force exerted on the system, the system exerts an equal and opposite force. The first force does work on the system, and the second does work by the system. Since the forces exerted ON and BY are equal and opposite, the work done ON and BY the system is equal and opposite.
The friction exerted on the domino sliding across the table is opposite the direction opposite its motion, and does negative work ON the system. The friction exerted by the domino on the table is in the direction of motion, and the positive work done by this force is done BY the system.
If an object is rising the the downward gravitational force exerted ON the object by gravity is opposite the direction of the rise, so gravity does negative work ON the object. The object exerts an equal and opposite gravitational force, which is in the direction of its rise, so the work done BY the system against gravity is positive.
In some cases it's easier to think in terms of the force exerted ON a system. If you're pushing something then you naturally experience the force exerted ON the system consisting of that object. In this case, even if you really want to find the work done BY the system, it's natural to calculate the work done ON the system and then take the negative of that result.
On the other hand if you are the system it question, then the force you exert is the force exerted BY the system. Assuming that it's more natural for you to think in terms of the force you exert, then it's more natural to find the force exerted BY the system. If you wanted the work done ON the system you would then take the negative of the work done BY the system.
If gravitational force is involved, it's most natural to put yourself in the position of the gravitational force and to figure out the work done ON a system by the gravitational force. If you then want the work done BY the system against the gravitational force (i.e., the PE change) then you would take the negative of the work done ON the system by that force.
The second question I have is on the experiment analysis you gave us to do. I am a little unclear on what we need to do. I think you want us the use the data from the ramp and ball we did the other day and find the new KE, using the new equation. We also need to find the velocity in the horizontal direction, and redo them with a 1 cm drop on the ramp. Is that correct?
The third qusetion I have is: delta y is always negative for the use in the equation right?
`dy is generally used for the change in vertical coordinate. The vertical coordinate can change upward or downward, so `dy could be positive or negative.